Condensate purification process

ABSTRACT

A CONDENSATE PURIFICATIN PROCESS INVOLVING DEMINERALIZATION IN A MIXED BED EXCHANGER UNDER CONDITIONS MINIMIZING ALKALI METAL LEAKAGE BY PREVENTING THE PRESENCE OF ALKALI FORM OF THE CATION EXCHANGE RESIN IN THE DEMINERALIZER. THE RESINS ARE SEPARATED INTO LAYERS AND REGENERATED IN DIFFERENT VESSELS OR IN THE SAME VESSEL. MINOR AMOUNTS OF CATION EXCHANGE RESIN ARE UNAVOIDABLY PRESENT IN THE ANION EXCHANGE RESIN DURING ITS REGENERATION BY ALKALI, AND THE SODIUM FORM OF THIS SMALL AMOUNT OF CATION EXCHANGE RESIN IS TRANSFORMED INTO THE AMMONIUM FORM BY RECIRCULATION OF AMMONIUM HYDROXIDE THROUGH THE ANION EXCHANGE RESIN AND THE MAIN BODY OF THE SPENT CATION EXCHANGE RESIN BEFORE ITS REGENERATION. THE SODIUM FROM THE ANION EXCHANGE RESIN IS DISPLACED INTO THE CATION EXCHANGE RESIN AND ELIMATED WHEN THE LATTER IS REGENERATED BY ACID.

June 1971 I G. J. cRrrs CONDENSATE PURIFICATION PROCESS Filed Sept. 25,1968 uwdmOhw 25mm mObEwzuowm 20-24 my E04 INVENTOR GEORGE J. CRITSATTORNEYS United States Patent Oifice US. Cl. 210-32 7 Claims ABSTRACTOF THE DISCLOSURE A condensate purification process involvingdemineralization in a mixed bed exchanger under conditions minimizingalkali metal leakage by preventing the presence of alkali form of thecation exchange resin in the demineralizer. The resins are separatedinto layers and regenerated in different vessels or in the same vessel.Minor amounts of cation exchange resin are unavoidably present in theanion exchange resin during its regeneration by alkali, and the sodiumform of this small amount of cation exchange resin is transformed intothe ammonium form by recirculation of ammonium hydroxide through theanion exchange resin and the main body of the spent cation exchangeresin before its regeneration. The sodium from the anion exchange resinis displaced into the cation exchange resin and eliminated when thelatter is regenerated by acid.

CROSS-REFERENCE TO RELATED APPLICATIONS The subject matter of thisapplication constitutes an improvement over the subject matters of thepatent to Applebaum and Crits, No. 3,414,508, dated Dec. 3, 1968, andthe patent to Crits and Zahn, 3,385,787, dated May 28, 1968. The subjectmatter may also involve procedures disclosed in Crits application Ser.No. 699,940, field Jan. 23, 1968, and Crits Pat. No. 3,455,819 datedJuly 15, 1969.

FIELD OF THE INVENTION This invention relates to a condensatepurification process involving ion exchange with the maintenance of anammonia content in a recirculatory system particularly adapted for thehandling of high flow rates of the condensate. The invention isparticularly applicable to steam turbine power plants.

DESCRIPTION OF THE PRIOR ART In a steam turbine power plant system it isof great importance to provide water for steam generation which issubstantially completely free of solid content which, if present, wouldproduce coating of surfaces within the turbine and boiler and elsewhere.Even though condensate is recirculated in the system to supply a boiler,there is always accumulation of solid solutes due to the necessity forproviding makeup water, possible leakage into the condenser, andsolution of metal.

In accordance with the foregoing patent of Applebaum and Crits,minimizing of sodium leakage is achieved by separation of the anionexchange resin from the cation exchange resin in either of two fashions:

In one case, flows are provided under conditions in which part of theanion exchange resin is, essentially, not regenerated, the portion notregenerated being above and adjacent to the cation exchange resin andforming a barrier to lessen the possibility that any sodium will enterthe cation exchange resin.

In an alternative process, the major part of the anion exchange resin isdelivered to a separate vessel in which it is regenerated with causticsoda and thoroughly washed before being admixed with the cation exchangeresin.

However, unless extreme precautions are taken in the 3,583,908 PatentedJune 8, 1971 matter of eifecting layering of the resins, there will bean appreciable content of cation exchange resin in what shouldtheoretically be only anion exchange resin. Therefore, when the anionexchange. resin is regenerated with caustic soda, the cation exchangeresin which it contains is transformed to the sodium state. Then whenadmixture occurs, this transformed cation exchange resin may becomelocated throughout the mixed bed, and when the condensate containingammonia passes therethrough some of the sodium is displaced by ammoniato enter the steam system. Under practical conditions of operation, inwhich extreme care cannot be exercised, and in which it is undesirableto waste too much anion exchange resin by using it to form a thickbarrier, the content of cation exchange resin in the anion exchangeresin may reach an amount of one percent or more. This is an appreciableamount and gives rise to sufficient sodium leakage to be objectionablein the power plant.

What has been described is improved by the adoption of an additionalstep in the process described in Crits and Zahn Pat. 3,385,787. Inaccordance with that patent the anion exchange resin eithersubstantially isolated from, or completely separated from, the main bodyof the cation exchange resin (through containing the small amount of thecation exchange resin) is regenerated with caustic soda and then rinsedfree of caustic soda in solution. But it is then treated with ammonia insolution using relatively high amounts and low concentrations ofammonia. The sodium form of the cation exchange resin, formed by thecaustic treatment, is then transformed to the ammonia form withproduction of sodium hydroxide which is washed out by excess ammoniasolution and then finally with water. The content of cation exchangeresin transformed to the ammoniated form is then in the condition inwhich it should finally be, and the anion exchange resin containing theammoniated cation resin may be returned to admixture with the majorcation exchange resin to provide the mixed bed demineralizing exchanger.Because of the small amount of cation exchange resin which must be giventhe massive treatment with ammonia, the additional treatment ispractical and economical.

SUMMARY OF THE INVENTION The present invention improves what has beendescribed by adoption of a different procedure. Ammonia is introducedinto the anion exchange resin, but after its introduction recirculationis effected through the anion exchange resin in series with the spentcation exchange resin, the regeneration of which is deferred. By thisrecirculation sodium is displaced from the residual cation exchangeresin contained in the anion exchange resin and enters the main body ofthe cation exchange resin which still has the capability of absorbingthis sodium. By reason of the recirculation, the amount of ammonianecessary is substantially reduced. The recirculation is carried out fora sufiicient time to reduce to a desired degree leakage of sodium fromthe anion exchange resin, the sodium form of the cation exchange resincontained in the anion exchange resin being converted, to a major extentinto the ammonium form.

The cation exchange resin is then regenerated by acid and rinsed,whereby sodium is substantially completely removed from the system. Bothresins are then mixed to provide the mixed bed for demineralization.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram illustratinga preferred system provided in accordance with the invention; and

FIG. 2 is a diagram showing a separator and regeneration vessel whichmay be used in accordance with another embodiment of the invention.

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, aplurality of mixed bed exchangers are used, operating in parallel,exhaustion taking these exchangers out of operation in sequence forshort periods of time as will appear hereafter. The invention isapplicable particularly to demineralization of a steam turbine powerplant, and typically the demineralized output from the exchangers willbe supplied through heat exchangers to a boiler providing steam to aturbine exhausting into a condenser. The condensate enters theexchangers to which make-up water is also fed. A single mixed bedexchanger is illustrated at 2, but it will be understood that usuallythis will be only one of a plurality of such exchangers operating inparallel. From the standpoint of the present invention, operations withrespect to one exchanger only need be described. The on-stream inlet andoutlet connections are indicated at 3 and 4. In general, in this figure,connections are primarily conventionalized with some valves indicated,but with pumps and other auxiliary devices omitted. Actual connectionsmay take many forms and it will be readily understood by those skilledin this art that proper connections are provided to produce the 'variousflows which will be described.

The exchangers are not called upon to take part in the actualregeneration (and accordingly may be active for longer duty cycles), butregeneration uses auxiliary tanks, the principal one of which is theseparator and cation regenerator 6. This is illustrated as in acondition containing both the anion exchange resin 8 and the cationexchange resin 10 in separated condition, the interface being indicatedat 9. The respective resins are of different specific gravities as isusual when stratification is desired, the anion exchange resin beinglighter than the cation exchange resin. Various resins may be used. Theanion exchange resin is of the hydroxyl type adapted to be regeneratedby caustic soda, while the cation exchange is of the hydrogen type,adapted to be regenerated by a strong acid, such as sulfuric acid,though in the present instance it is used in ammoniated form as willpresently appear. The usual support, conventionalized as a screen 12,prevents outflow of the resins from the bottom of the tank. Pipeconnections '14 and 16 are connected to pipe 17 running to a line 18through which, as will be indicated later, the resins are caused to flowin aqueous suspension.

Each of the exchangers is provided with upper and lower passages 20 and22 for inflow and outflow of the resins, the resins being carried on thesupport 24 which may take many of the usual conventional forms toprevent outflow of the resins with the water being treated. Theconnections 20 and 22 run with suitable valving to the line 18. Theseparator 6 is provided with inlets 26, 28 and 30, respectively for air,water and acid regenerant. Drain and vent connections of conventionaltype are not illustrated.

A connection 32 for introduction of water communicates with adistributor 34 which may consist of an array of pipes containingperforations preventing outflow of resins. A sluice 36 is shown in theform of an elbow with the upper open end 38 located below thedistributor 34 and preferably at a level such as indicated spaced by adimension D above the normal interface 9 between the anion and cationexchange resins when they are stratified. This dimension may range,desirably, from about one inch to three inches. A greater value for D isgenerally unnecessary and merely represents some wastage of anionexchange resin 8. The dimension D is merely to insure a minimumpercentage of cation exchange resin in the anion exchanger region of theseparator.

In practical operation, the interface 9 may Well be rather indefinite,there being in the vicinity of the interface some admixture of theresins, with conditions varying in successive steps of operation.

The sluice 36 communicates at 40 through a valve with the upright pipe17.

The anion exchange resin is regenerated separately from the cationexchange resin, and for this purpose there is provided the separateregeneration vessel 42, the upper end of which is connected at 44through a valve with the line 17. Water may enter the top of the vessel42 at .46, and ammonia in aqueous solution may enter at 47. At the topof the vessel there is also provided the line 48 for entry of causticregenerant. A drain 50 is indicated. At 52 there is a valved connectionbetween the lower portion of the vessel 42, above the perforated support54, and the pipe 17.

There is also desirably provided a separate resin storage tank 56 fortemporarily holding the mixed resins which have been regenerated. At thetop of the tank there is provided an inlet 58 for ammonia (in aqueoussolution) and at the bottom of the tank there is an outlet 60 connectingthrough pipe 62 to the line 18 previously mentioned. The top of the tankis connected at 64 to the same line. Suitable valving is provided. Theline 18 has a valved drain connection 66. Additionally illustrated arewater connections 68 and respectively at the top and bottom of the tank,a vent connection 72, and a lower air inlet connection 74.

What has been so far described is apparatus and connections disclosed insaid Crits and Zahn patent. In accordance with the present inventionthere are provided other connections and elements for the ammoniarecirculation and sampling as follows:

A valved connection 61 runs from the bottom of the anion regenerator 42to the top of the separator 6. A sampling connection is provided by avalve 63 to a pipe 65 for the Withdrawal of samples to ascertain thesodium leakage and ammonium concentration issuing from the anionregenerator. A valved connection 67 from the bottom of the separator 6runs to a pump 69 which delivers the recycled ammonia through connection71 to the top of the anion regenerator 42. From the line 71 there runsthe sampling connection provided with a valve 73 for the purpose ofsampling for measurement of sodium and ammonia concentration.

Operation is as follows:

When one of the battery of exchangers requires regeneration, it is takenoff the line and the mixed resins therein are transferred through theoutlet 22 and by way of the line 18 into the empty separator 6 throughthe connection 14. When this transfer is completed, resin from thestorage tank 56, in the regenerated state, may be immediatelytransferred by way of connection 60 and lines 62 and 18, and connection20, into the exchanger and it may be put back into active operation. Bythis arrangement the down-time of any exchanger is minimized and it neednot be out of operation during the regeneration of its resins.

The mixed resins in the separator are desirably first backwashed whilein the mixed state, to separate the resin granules and to remove thesolids which were filtered out during on-stream operation. Thebackwashing may comprise upward fiow of water at suitable velocity,alternating with drainage and air flow to produce scrubbing. After thesolids, including metal oxides, are effectively removed, the Water flowmay be stopped as usual to provide sedimentation of the resins and theirStratification to the condition illustrated in FIG. 1, in which theanion exchange resin 8 overlies the cation exchange resin 10' with theinterface 9 located, preferably, below the open end 38 of the sluice 36,the spacing involving the dimension D previously described.

The scrubbing may alternatively be carried out in accordance with theprocedure described in Crits Patent No. 3,455,819.

The next step involves transfer of the anion exchange resin 8 to theanion regenerator 42. This is effected by opening the connections at 40,17 and 44 to provide delivery of the resin, water being introduced at 32to pro vide fiuidizing of the resin 8 so that the fluent suspension willflow through the sluice 36. That portion of resin above the level 38will thus be transferred, the small amount between the top of the sluiceand the interface 9 remaining in the separator 6. What is desired hereis a transfer of the anion exchange resin with a minimum content of thecation exchange resin.

Following the transfer of the resin 8, separate regenerations of the tworesins are effected, but in accordance with the present invention theregeneration of the cation exchange resin is deferred.

The anion exchange resin is regenerated in the vessel 42 by treatmentwith caustic soda entering at 48. This part of the regeneration iscarried out in conventional fashion utilizing the proper amount ofcaustic soda, and then thorough rinsing is effected to remove thecaustic soda in solution.

Despite careful Stratification and the presence of a barrier portion ofthe anion exchange resin in the region having the dimension D, it ispractically impossible to eliminate all cation exchange resin from theanion exchange resin Which is treated in the anion regenerator 42. Thestratification is not even perfect with respect to resin particles ofnormal size; but inevitably there are fines of cation exchange resinwhich, because of their small size, settle more slowly, and these remainin the anion exchange resin. In practical operation it is difiicult toreduce the percentage of cation exchange resin in the material in theanion regenerator below about one percent, and several percent mayordinarily be present. In the regeneration with caustic soda, thisresidual cation exchange resin is transformed to its sodium state. Theaffinity of cation exchange resin for sodium and for ammonium issufiiciently close that during on-stream operation with the condensatecontaining ammonia, appreciable amounts of the sodium will be displacedto appear in the treated water. This is particularly true when it isconsidered that the resins are mixed in the exchangers and thereforeappreciable amounts of the sodium form of the cation exchange resin willbe near the bottom of the mixed bed. In accordance with the disclosureof the Crits and Zahn patent, after regeneration by the caustic soda andrinsing, ammonia in aqueous solution was introduced at 47 and theefiluent discarded through the drain 50. By massive treatment by ammoniaat this point, the ammonium replaced the sodium to reduce the sodiumcontent to a negligible amount.

This treatment involved a considerable loss of ammonia.

In accordance with the present invention saving of ammonia is achievedas follows:

Following the rinsing out of the caustic soda in solution, theconnections 61 and 67, 71 are opened with operation of pump 69, and alimited amount of ammonia in suitable concentration is introduced ateither 47 or 31, followed by recirculation by the pump 69 through thevessels 42 and 6 in series. By reason of this recirculation, the ammoniagradually removes the sodium from the cation exchange resin in the anionexchange resin contained in the vessel 42, and this sodium accumulatesin the cation exchange resin in the vessel 6. While this cation exchangeresin is exhausted from the standpoint of onstream operation, and is duefor regeneration, it still retains substantial ability to absorb sodium.The recirculation is carried out until tests of samples withdrawn at 65indicate that there is adequately low leakage of sodium from the anionregenerator, which means that the residual cation exchange resin hasbeen adequately transformed to its ammonium form, which is the formwhich is ultimately desired in any event. Tests of samples withdrawn at75 will furnish further indications of the conditions involved and ofthe ammonia concentration in the recirculated liquid.

After the desired conditions are achieved, the cation exchange resin 10is regenerated in the separator 6 by the upward or downward flow of acidregenerant (usually sulfuric acid solution). Following this, the usualrinsing may be effected either by downflow of water from the connection32 or upflow from the connection 28. The rinsing water is discharged inthe usual fashion. This regeneration removes from the system the sodiumwhich originated in the cation exchange resin dispersed through theanion exchange resin. The cation exchange resin 10 is thus left in itshydrogen state; but if desired it may be ammoniated by introduction ofammonia in solution at 31.

Following the regeneration of both resins, the anion exchange resinbeing in its hydroxyl state, and the entrained cation exchange resinbeing primarily in its ammoniated state, and the cation exchange resinbeing either in its hydrogen form or its ammonium form, if the latter isproduced, both of them are caused to flow into the resin storage tank 56by connections which will be obvious. As introduced into this tank, thetwo resins may be substantially separated; but by the introduction ofwater and air under conditions of reasonably violent flow, goodadmixture may be obtained.

After admixture is achieved, it is desirable to effect ammoniation ofthe cation exchange resin, and for this purpose ammonium hydroxide maybe introduced at 58 if ammoniation had not formerly occurred in tank 6.However, this ammoniation may be deferred, the mixed resins beingdelivered to an exchanger 2 with ammoniation either effected therein or,gradually, by adding ammonia to the system at any suitable point.Ultimatel the cation exchange resin will be in its ammoniated state.

Through the use of the storage tank 56, there is provided a receptaclefor the regenerated resins, despite the fact that the exchanger fromwhich the resins were obtained is back in use. This leads to the moreeffective duty cycle of the exchangers.

However, it will be evident that the vessel 6 could have its functionsprovided by suitable construction of a mixed bed exchanger; i.e., eachmixed bed exchanger could function as the separator and cationregenerator. A separate anion regenerator could be provided asdescribed, and after anion regeneration was effected therein the anionexchange resin could be transferred back to the mixed bed exchanger inwhich mixing could be effected. In such case the resin storage tankwould be unnecessary. However, it will be evident that the mixed bedexchanger would then, for best results, have a more elaborateconstruction as illustrated for the separator 6, and generally operationin this last fashion is not desirable.

If it is permissible to have one of a battery of mixed bed exchangersout of operation for a more prolonged period, the resin storage tank maybe eliminated, the resins after regeneration being returned to theexchanger from which they came, with admixture therein.

Another alternative operation may involve regeneration of both resins inthe same separation vessel, and the use of this procedure is exemplifiedin FIG. 2. In that figure the separator and regeneration vessel may beregarded as replacing both of the vessels 6 and 42 of FIG. 1, with theunderstanding that the vessel 80 is associated with a bank of mixed bedexchangers 2 and with a resin storage tank 56.

The vessel 80 is shown as containing the layered anion exchange resin 82and cation exchange resin 84, separated by the interface 86. Locatedwithin the anion exchange resin is a collector 88 which may take theform of a network of pipes having small perforations preventing outflowof resin particles to a waste connection 90. The collector 88 is locatedabove the interface 86, being spaced thereabove to the same extent asthe open upper end 38 of the sluice 36 was spaced above thecorresponding interface in FIG. 1, i.e., about one inch in the case oftanks of small cross-section up to about three inches for larger tanks,i.e., the spacing D to provide a barrier layer of the anion exchangeresin to minimize content of cation exchange resin in the upper layer.

The upper end of the vessel 80 is provided with a connection 92 whichmay involve inflow and outflow during operation, there being alsoprovided the outflow connection 94 above the support 95 which holds theresins but permits inflow and outflow of liquids. The connection 94functions primarily for the removal of the resins.

At the upper end of the vessel 80 there are indicated various flowpassages which, of course, can be constituted by a single or a lessnumber of passages with obvious valving, the passages being indicated asindependent to simplify description of operation. The passages comprisethe vent 96, a water inflow passage 98, a caustic regenerant passage100, and an ammonia passage -2.

At the bottom of the vessel below the resin support 95 there areindicated individual passages which also may be provided by a singlepassage with suitable valving. The passages indicated are the drain 104,the passage 106 for upward or downward flow of water, the air passage108, acid regenerant passage 110, and ammonia passage 112.

For the purpose of the present invention a recirculation system isprovided involving the connection 114 from the bottom of the vesselrunning to a pump 116 which, through connection 118 provides delivery ofammonia solution to the top of the vessel 80. A sampling connection 120controlled by a valve 122 may take samples from the connections 114,118. Additional sampling may be from the outlet 88.

The operation of this modification is as follows:

The vessel 80 is empty between regenerations. When one of the exchangersof the bank requires regeneration of its resins, it is taken out ofservice and the mixed resins therefrom are delivered to the vessel 80*.Immediately after this, the emptied exchanger may receive a new chargeof mixed resins from the storage vessel and be restored to service. Thisis as described with reference to FIG. 1.

The next operation is backwashing and scrubbing of the resins nowcontained in vessel 80, still in mixed form. For this purpose water isentered at 106 and discharged through connection 92', then connected towaste. Water flow may be alternated with introduction of air to insuregood cleaning, this involving removal of dirt including metal oxidesseparated by the filtering action in the exchanger. The alternativescrubbing procedure of Crits Patent No. 3,455,819 may be used.

Following this washing and scrubbing the water flow is stopped toprovide the settling and stratification of the resins, which attain thestate indicated in FIG. 2. with a fairly well defined interface 86. Theanion exchange resin as described in connection with the previousmodification, will contain even above the level of the piping 88 somecation exchange resin in the nature of fines as Well as some entrainedparticles of larger size.

Regeneration of the anion exchange resin is effected by producingdownward flow of the caustic regenerant through the passage 100, thiscaustic regenerant flowing outwardly to waste through the connection 90.To prevent as far as possible entrance of the caustic regenerant intothe cation exchange resin, it is desirable to provide an upward flow ofwater through connection 106 which water also flows out throughconnection 90. This prevents substantial regeneration of the portion ofthe anion exchange resin between the collector 88 and the interface 86,but this waste of the anion exchange resin can be tolerated for the sakeof prevention of entrance of sodium into the cation exchange resin.

The next step is rinsing with water entering at 98 while maintaining thebarrier flow of water through 106; both flows pass through connection 90to waste. This gets rid of excess sodium hydroxide.

The small amount of cation exchange resin in the region '82 will now bein its sodium form which is objectionable as previously discussed.

Treatment with ammonia now takes place. The required amount of ammoniais introduced at 102 (or 112) and then recirculation is effected byopening the connections 114 and 118 and operating the pump 116. Theeffect is substantially what has been described in connection with FIG.1: the ammonia is recirculated through the anion exchange bed 82 and thecation exchange bed 84, in series, displacing sodium from the cationexchange resin dispersed through the bed 82, with absorption of thesodium in the cation exchange bed 84 which still retains the capabilityof such absorption. During this recirculation the waste outlet 90 isclosed except for the possible withdrawal of samples to indicate theamount of residual sodium leakage from the bed 82. Samples may also bewithdrawn at 1'20 to test the adequacy of the ammonium content andleakage of sodium from the bottom of bed 84.

After the recirculation is terminated, and the recirculation connectionsclosed, a water rinse of the beds is desirable.

The next step involves the regeneration of the cation exchange resin 84,and this may be carried out in usual fashion with sulfuric acidintroduced at 110. Excess regenerant is caused to flow out through thewaste connection 90, while barrier water is caused to flow downwardlyfrom connection 98 through the upper portion of the anion exchangeresin. This serves for further rinsing of the anion exchange resin.

The acid regeneration will remove the sodium accumulated in the cationexchange bed 84 and also what may exist in the portion of the bed 82below the outlet 90.

Following the acid regeneration, rinse water is caused to flow throughconnection 106 while the barrier flow through connection 98 iscontinued, the flow being outward through connection 90.

While as indicated above, ammoniation of the cation exchange resin maybe effected otherwise, the last rinsing step may be followed by upwardflow of ammonium hydroxide through connection 112 to ammoniate the bed84.

Following this, mixing may be effected, and the mixed resins may then bedelivered from the vessel to the resin storage tank. The mixing may beeffected in the latter if desired, and the ammoniation may be effectedtherein.

Alternatives to what has been described may involve the elimination ofthe resin storage tank; In such case, the exchanger may be keptinoperative during regeneration of its resin, and after regeneration asdescribed, the mixed resins may be returned to the exchanger.

Still another modification may involve the construction of eachexchanger to provide regeneration in itself, there being provided thecollector arrangement as at 88, this, during on-stream operation, beingclosed off. In such case, of course, on-stream connections would beinvolved in addition to those indicated in FIG. 2.

In the foregoing procedural sequences have been described withoutparticular references to concentrations, quantities of materials, or thelike. These factors are essentially common to the alternative procedureswhich have been described and may, accordingly, be considered as aunitary matter.

The regeneration of the anion exchange resin by sodium hydroxide (orother alkali) may be carried out in a fashion generally conventional,and, as is conventional, the amount of sodium hydroxide used may varyfrom about twelve to fifteen pounds per cubic foot of the anion exchangeresin. This amount may vary to a great extent depending upon particularcircumstances involved as will be evident to those skilled in the art,and concentrations of the sodium hydroxide are quite arbitrary. Theparticular conditions of regeneration are not of substantial relevanceto the matters involved in the present invention. For proper results itis important that the rinsing following the regeneration of the anionexchange resin should be carried out sufficiently to minimize sodium insolution, and the completeness of effective rinsing may be determined inthe usual fashion by measurement of the conductivity of the effluent.

The conditions involved in the recycling of the ammonium hydroxide aresusceptible to a Wide range of choice, but typically the following maybe cited as examples of what have been found to be optimum conditions:

The concentration of the ammonium hydroxide (as NH may well be in therange of 0.1% to 3.0%, through these limits may be exceeded. Highlyeflective concentrations have been found to be in the range of 0.2% to0.6%.

The quantity of NH may be of the order of one hundred pounds or less percubic foot of the cation content in the anion exchange resin.

The recirculation rate of the ammonium hydroxide may be of the order ofthree to ten gallons per minute per square foot of horizontal crosssection of the anion resin bed. Here also the rate may well exceed theselimits; it less, the recycling may occupy a longer time; if more, therate may be such that the lessening of the time of recycling may not besignificant.

Recycling is generally desirably continued for a time necessary toreduce the sodium leakage from the anion exchange resin to one part permillion or less, depending upon What is desired.

The conditions just described have been found to result in recycling forperiods of the order of five to twelve hours. Conditions involved may bein accordance with the disclosure of Crits application Scr. No. 699,940,referred to above.

The amount of ammonium hydroxide required in accordance with theinvention is much less than that required if the anion exchange resin istreated without recycling through the spent cation exchange resin. Ifthe recycling is not used, the ammonium hydroxide, containing sodium,must be run to waste, since in passing through the anion exchange resinmuch of it is not effective to displace sodium, whereas if recycling isused the effective contact of the ammonium hydroxide with the sodiumform of the entrained cation exchange resin is increased.

The regeneration of the cation exchange resin by sulfuric or other acidmay be carried out in usual fashion, i.e., using around fifteen poundsof sulfuric acid per cubic foot of the cation exchange resin, or theequivalent of other acid.

I claim:

1. In a water purification process involving flow of water through ademineralizer containing mixed anion exchange resin granules and cationexchange resin gran ules of different densities, the steps of separatingthe resins into two beds one of which contains anion exchange resingranules entraining a minor amount of cation exchange resin granules andthe other of which contains the major part of the cation exchange resingranules, regenerating with alkali only the first mentioned bed, rinsingalkali from the first mentioned bed, recirculating ammonia through bothbeds in series to effect displacement of alkali metal from the entrainedcation exchange resin granules into the second mentioned bed,regenerating 10 with acid the second mentioned bed, and removing excessof acid regenerant from the second mentioned bed.

2. The process of claim 1 in which the granules of cation exchange resinhave a higher specific gravity than those of the anion exchange resin,in which the separation of the resins provides a lower layer ofprimarily the cation exchange resin granules and an upper layer ofprimarily the anion exchange resin granules with upper and lowerportions of said upper layer, with the lower portion of minor volumelocated above the lower layer to isolate the upper portion therefrom,said upper portion forming said first mentioned bed, and at least saidlower layer forming the second mentioned bed.

3. The process of claim 2 in which the alkali regeneration of the firstmentioned bed is effected while it is isolated from said lower portionof the upper layer.

4. The process of claim 2 in which the alkali regeneration of the firstmentioned bed and the subsequent treat ment with ammonia are effectedwhile the granules of that bed rest on said lower portion of the upperlayer.

5. In a water purification process involving flow of water through ademineralizer containing anion exchange resin granules, and cationexchange resin granules of relatively higher density than the anionexchange resin granules, the steps of separating the resins into twobeds with the cation exchange resin granules forming the lower bed andthe anion exchange resin granules along with a small amount of entrainedcation exchange resin granules forming the upper bed, regenerating withalkali the anion exchange resin granules of the upper bed, treating Withammonia the regenerated anion exchangeresin granules while separatedfrom the lower bed to displace, by ammonium, sodium from the cationexchange resin entrained with the anion exchange resin, said treatmentwith ammonia involving recirculation of the ammonia through both beds inseries, then regenerating with acid the cation exchange resin granulesof said lower bed, removing excess of acid regenerant from said lowerbed, and ammoniating the cation exchange resin granules regenerated withacid.

6. The process of claim 5 in which the alkali regeneration of the anionexchange resin granules of the upper bed and the subsequent treatmentthereof by ammonia are effected while the granules of that bed areisolated from the lower bed.

7. The process of claim 5 in which the alkali regeneration of the anionexchange resin granules of the upper bed and the subsequent treatmentthereof by ammonia are effected while the granules of that bed rest onthe lower bed.

References Cited UNITED STATES PATENTS 3,385,787 5/1968 Crits et al210-32 3,414,508 12/1968 Applebaum et a1. 210--37X 3,438,891 4/1969Schmidt et a1. 210-32 SAMIH N. ZAHARNA, Primary Examiner U.S. Cl. X.R.21035

